1. Field of the Invention
The present invention relates to a method of measuring and compensating the eccentricities of the backup rolls of a rolling mill for correcting the thickness variations of a rolling plate caused by the eccentricities of the backup rolls.
2. Description of Prior Arts
A rolled plate with uniform thickness and flatness from a rolling mill is a goal constantly pursued by many steel plate manufacturers. Among the various factors which affect the thickness and flatness of the rolling plate, eccentricity of the backup roll is most decisive. Many systems and methods have been proposed and devised therefore for compensating the roll eccentricities to minimize the thickness variations of the rolling plates. And many of them have been disclosed in the U.S. patents, such as U.S. Pat. No. 4,222,254 to King et al, Pat. No. 4,648,257 to Oliver et al, or Pat. No. 4,299,104 to Hayama et al . . . etc. Typically, the prior arts including the foregoing disclosures can be categorized into the three following methods:
(a) Fourier series method: This method takes the measurement of the cyclic thickness change of a rolling plate as a time-domain waveform and utilizes the Fourier transform technique to find the corresponding amplitudes and phases which are used as the compensation signals to be sent to an automatic gauge control system to correct the thickness variations of the rolling plate caused by the roll eccentricity.
(b) Total eccentricity lookup table method: This method firstly builds an eccentricity table off-line by rotating the backup rolls a full cycle and records the eccentricity values of a number of points on the peripheries of the backup rolls.
(c) Bandpass filter method: This is an on-line method which regards the angular velocity of the backup rolls as the frequency component, and designs a bandpass filter, with the center frequency of the pass band being the angular velocity, to extract the rolling force signals and convert the signals into the controlling signals to control the rolling force.
Among these methods, the Fourier transform method has the drawback of a less precise controlling signal since that only the fundamental frequency, ignoring the many other existing harmonics, is extracted to control the thickness variations of the rolling plate. Moreover, the system is also expensive to implement and difficult to maintain. The lookup table method, on the other hand, offer a more precise rolling plate, but it still has the drawback that the building of the enormous lookup table is quite time-consuming and tedious. The on-line methods are suited only for the products which require continuous rollings, such as cold and hot rolling.